This invention relates to compositions and methods for preserving plants and plant parts. In particular, it relates to compositions comprising substituted urea compounds (e.g., thidiazuron) to inhibit senescence in plants.
Leaf yellowing is a common symptom of the onset of leaf senescence in plants, and is often a problem in horticulture or other agricultural production systems (Funnell, K. A., et al., Hortscience, 33:1036-103 (1998); Tollenaar, M., Crop Science, 31(1):119-124 (1991)). Yellow leaves are unsightly and reduce the quality, value and shelf life of ornamentals such as potted roses, potted and cut lilies, flowers of Alstroemeria, and leafy vegetables (Tjosvold, Steven A., et al., Hortscience, 29:293-294 (1994); Staby, G. L., et al., Florists Rev., 161:38 (1977); Hibma, J. T., Verslag Centrum voor Agrobiologisch Onderzoek, 91:26 (1988)). Early onset of leaf senescence can affect agricultural productivity in diverse ways, for example yield in grain and legume crops and success of propagation of leafy cuttings (Martin del Molino, I. M., et al., Physiol. Plant, 66(3):503-508 (1986); Caldiz, et al., Plant Growth Regulation, 10(3):197-204 (1991); Finnan, J. M., et al., Agriculture Ecosystems and Environment, 69:27-35 (1998)).
Application of the synthetic cytokinin, benzylaminopurine (BAP) to leaves is known to prevent leaf yellowing and senescence (Richmond, A. E., et al., Science, 125:650-651 (1957); Dyer, T. A., et al., Journal of Experimental Botany, 22:552-560 (1971); Gan, S., et al., Bio Essay, 18:557-565 (1996)) This material along with Gibberellic acid (GA, another plant hormone with anti-senescence activity) are now in commercial use to prevent leaf yellowing in cut chrysanthemum flowers and potted roses, among others (van Doom and de Wit, 1992; Tjosvold, Steven A., et al., Hortscience, 29:293-294 (1994); Han, S. S., Journal of the American Society for Horticultural Science, 122::869-872 (1997); Funnell, K. A., et al., Hortscience, 33:1036-103 (1998)). 
The compound is registered for use as an herbicide and defoliant. It has high activity as a cytokinin, which probably is the basis of its herbicidal and defoliation properties. It is commonly used as substitute for BAP, zeatin, and other cytokinins that are used in plant tissue culture, because of its high activity (10 to 100 times that of BAP) and because plants do not metabolize it (Genkov, T., Bulgarian Journal of Plant Physiology, 21:73-83 (1995) and Murthy In vitro Cellular and Developmental Biology Plant 34::267-275 (1998)).
There is a real and continuing need for effective preservation formulations to inhibit senescence of leaves and other chlorophyll-containing plant organs. Such formulations can be used, for example, to preserve fresh cut flowers or potted plants. The present invention addresses these and other needs.
This invention provides compositions and methods for preserving plants, such as plant parts (e.g., cut flowers) and potted plants. The methods are based on the observation that compounds of Formula I are useful to prevent senescence in plants, particularly in chlorophyll-containing tissues. For example, the compounds maintain leaves in cut flowers or potted plants. In addition, in potted plants the compounds of the invention enhance growing buds and maintain flowers. 
wherein:
R1, and R4 are independently selected from the group consisting of hydrogen and lower alkyl,
R2 and R3 are independently selected from the group consisting of substituted or unsubstituted alkyl, substituted or unsubstituted cycloalkyl, substituted or unsubstituted aryl, and substituted or unsubstituted heteroaryl; and X is an oxygen or sulfur atom.
If R2 or R3 is alkyl it can be substituted or interrupted at least once by oxygen or sulfur. If R2 or R3 is cycloalkyl its can be substituted at least once by alkyl. If R2 or R3 is aryl substituted at least once by a member of the group consisting of alkyl, halogen, alkyl mercapto, alkoxy, trifluoromethyl and NR5R6, wherein R5 and R6 are independently selected from the group consisting of H or lower alkyl. In some embodiments R2 and R1 or 3 and R4 together with the N atom, form a heterocyclic or heteroaryl ring, such as a morpholino, a piperidino, or a pyrrolidino moiety.
A preferred compound to use in the methods is 1-phenyl-3-(1,2,3-thiadiazol-5-yl)urea, referred to as thidiazuron. Other preferred compounds include N-(2-chloro-4-pyridyl)-Nxe2x80x2-phenylurea and 1,3-diphneyl urea.
The compositions of the invention may contain other constituents such as plant nutrients and surfactants, depending upon the particular use. The methods are useful with all plants, particularly cut flowers and potted plants.
The term xe2x80x9cplantxe2x80x9d includes whole plants, and plant parts including shoot vegetative organs/structures (e.g. leaves, stems and tubers), roots, flowers and floral organs/structures (e.g. bracts, sepals, petals, stamens, carpels, anthers and ovules), seed (including embryo, endosperm, and seed coat) and fruit (the mature ovary). For example, the term refers to cut flowers or other organs. The class of plants that can be used in the method of the invention includes the class of higher and lower plants, including angiosperms (monocotyledonous and dicotyledonous plants), gymnosperms, ferns, and multicellular algae. It includes plants of a variety of ploidy levels, including aneuploid, polyploid, diploid, haploid and hemizygous.
The term xe2x80x9calkyl,xe2x80x9d by itself or as part of another substituent, means, unless otherwise stated, a straight or branched chain, or cyclic hydrocarbon radical, or combination thereof, which may be fully saturated, mono- or polyunsaturated and can include di- and multi-valent radicals, having the number of carbon atoms designated (i.e. C1-C10 means one to ten carbons). Examples of saturated hydrocarbon radicals include groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, t-butyl, isobutyl, sec-butyl, cyclohexyl, (cyclohexyl)ethyl, cyclopropylmethyl, homologs and isomers of, for example, n-pentyl, n-hexyl, n-heptyl, n-octyl, and the like. An unsaturated alkyl group is one having one or more double bonds or triple bonds. Examples of unsaturated alkyl groups include vinyl, 2-propenyl, crotyl, 2-isopentenyl, 2-(butadienyl), 2,4-pentadienyl, 3-(1,4-pentadienyl), ethynyl, 1- and 3-propynyl, 3-butynyl, and the higher homologs and isomers. The term xe2x80x9calkyl,xe2x80x9d unless otherwise noted, is also meant to include those derivatives of alkyl defined in more detail below as xe2x80x9cheteroalkyl,xe2x80x9d xe2x80x9ccycloalkylxe2x80x9d and xe2x80x9calkylene.xe2x80x9d The term xe2x80x9calkylenexe2x80x9d by itself or as part of another substituent means a divalent radical derived from an alkane, as exemplified by xe2x80x94CH2CH2CH2CH2xe2x80x94. Typically, an alkyl group will have from 1 to 24 carbon atoms, with those groups having 10 or fewer carbon atoms being preferred in the present invention. A xe2x80x9clower alkylxe2x80x9d or xe2x80x9clower alkylenexe2x80x9d is a shorter chain alkyl or alkylene group, generally having eight or fewer carbon atoms.
The term xe2x80x9calkoxy,xe2x80x9d refers to those groups having an alkyl group attached to the remainder of the molecule through an oxygen, atom.
The term xe2x80x9calkyl mercapto,xe2x80x9d refers to those groups having an alkyl group attached to the remainder of the molecule through a sulfur atom.
The terms xe2x80x9ccycloalkylxe2x80x9d and xe2x80x9cheterocycloalkylxe2x80x9d, by themselves or in combination with other terms, represent, unless otherwise stated, cyclic versions of xe2x80x9calkylxe2x80x9d and xe2x80x9cheteroalkylxe2x80x9d, respectively. Additionally, for heterocycloalkyl, a heteroatom can occupy the position at which the heterocycle is attached to the remainder of the molecule. Examples of cycloalkyl include cyclopentyl, cyclohexyl, 1-cyclohexenyl, 3-cyclohexenyl, cycloheptyl, and the like. Examples of heterocycloalkyl include 1-(1,2,5,6-tetrahydropyridyl), 1-piperidinyl, 2-piperidinyl, 3-piperidinyl, 4-morpholinyl, 3-morpholinyl, tetrahydrofuran-2-yl, tetrahydrofuran-3-yl, tetrahydrothien-2-yl, tetrahydrothien-3-yl, 1-piperazinyl, 2-piperazinyl, and the like.
The terms xe2x80x9chaloxe2x80x9d or xe2x80x9chalogen,xe2x80x9d by themselves or as part of another substituent, mean, unless otherwise stated, a fluorine, chlorine, bromine, or iodine atom. Additionally, terms such as xe2x80x9cfluoroalkyl,xe2x80x9d are meant to include monofluoroalkyl and polyfluoroalkyl.
The term xe2x80x9caryl,xe2x80x9d employed alone or in combination with other terms (e.g., aryloxy, arylthioxy, arylalkyl) means, unless otherwise stated, an aromatic substituent which can be a single ring or multiple rings (up to three rings), which are fused together or linked covalently. xe2x80x9cHeteroarylxe2x80x9d are those aryl groups having at least one heteroatom ring member. Typically, the rings each contain from zero to four heteroatoms selected from N, O, and S, wherein the nitrogen and sulfur atoms are optionally oxidized, and the nitrogen atom(s) are optionally quaternized. The xe2x80x9cheteroarylxe2x80x9d groups can be attached to the remainder of the molecule through a heteroatom. Non-limiting examples of aryl and heteroaryl groups include phenyl, 1-naphthyl, 2-naphthyl, 4-biphenyl, 1-pyrrolyl, 2-pyrrolyl, 3-pyrrolyl, 3-pyrazolyl, 2-imidazolyl, 4-imidazolyl, pyrazinyl, 2-oxazolyl, 4-oxazolyl, 2-phenyl-4-oxazolyl, 5-oxazolyl, 3-isoxazolyl, 4-isoxazolyl, 5-isoxazolyl, 2-thiazolyl, 4-thiazolyl, 5-thiazolyl, 1,2,3, thiadiazol-5-yl, 2-furyl, 3-furyl, 2-thienyl, 3-thienyl, 2-pyridyl, 3-pyridyl, 4-pyridyl, 2-pyrimidyl, 4-pyrimidyl, 5-benzothiazolyl, purinyl, 2-benzimidazolyl, 5-indolyl, 1-isoquinolyl, 5-isoquinolyl, 2-quinoxalinyl, 5-quinoxalinyl, 3-quinolyl, and 6-quinolyl. Substituents for each of the above noted aryl ring systems are selected from the group of acceptable substituents described below. The term xe2x80x9carylalkylxe2x80x9d is meant to include those radicals in which an aryl group is attached to an alkyl group (e.g., benzyl, phenethyl, pyridylmethyl and the like) or a heteroalkyl group (e.g., phenoxymethyl, 2-pyridyloxymethyl, 3-(1-naphthyloxy)propyl, and the like).
Each of the above terms (e.g., xe2x80x9calkyl,xe2x80x9d xe2x80x9cheteroalkylxe2x80x9d and xe2x80x9carylxe2x80x9d) are meant to include both substituted and unsubstituted forms of the indicated radical. Preferred substituents for each type of radical are provided below.
Substituents for the alkyl and heteroalkyl radicals (including those groups often referred to as alkylene, alkenyl, heteroalkylene, heteroalkenyl, alkynyl, cycloalkyl, heterocycloalkyl, cycloalkenyl, and heterocycloalkenyl) can be a variety of groups selected from, for example: xe2x80x94ORxe2x80x2, xe2x95x90O, xe2x95x90NRxe2x80x2, xe2x95x90Nxe2x80x94ORxe2x80x2, xe2x80x94NRxe2x80x2Rxe2x80x3, xe2x80x94SRxe2x80x2, -halogen, xe2x80x94SiRxe2x80x2Rxe2x80x3Rxe2x80x2xe2x80x3, xe2x80x94OC(O)Rxe2x80x2, xe2x80x94C(O)Rxe2x80x2, xe2x80x94CO2Rxe2x80x2, CONRxe2x80x2Rxe2x80x3, xe2x80x94OC(O)NRxe2x80x2Rxe2x80x3, xe2x80x94NRxe2x80x3C(O)Rxe2x80x2, xe2x80x94NRxe2x80x2xe2x80x94C(O)NRxe2x80x3Rxe2x80x2xe2x80x3, xe2x80x94NRxe2x80x3C(O)2Rxe2x80x2, xe2x80x94NHxe2x80x94C(NH2)xe2x95x90NH, xe2x80x94NRxe2x80x2C(NH2)xe2x95x90NH, xe2x80x94NHxe2x80x94C(NH2)xe2x95x90NRxe2x80x2, xe2x80x94S(O)Rxe2x80x2, S(O)2Rxe2x80x2, xe2x80x94S(O)2NRxe2x80x2Rxe2x80x3, xe2x80x94CN and xe2x80x94NO2 in a number ranging from zero to (2N+1), where N is the total number of carbon atoms in such radical. Rxe2x80x2, Rxe2x80x3 and Rxe2x80x2xe2x80x3 each independently refer to hydrogen, unsubstituted (C1-C8)alkyl and heteroalkyl, unsubstituted aryl, aryl substituted with 1-3 halogens, unsubstituted alkyl, alkoxy or thioalkoxy groups, or aryl-(C1-C4)alkyl groups. When Rxe2x80x2 and Rxe2x80x3 are attached to the same nitrogen atom, they can be combined with the nitrogen atom to form a 5-, 6-, or 7-membered ring. For example, xe2x80x94NRxe2x80x2Rxe2x80x3 is meant to include 1-pyrrolidinyl and 4-morpholinyl. From the above discussion of substituents, one of skill in the art will understand that the term xe2x80x9calkylxe2x80x9d is meant to include groups such as haloalkyl (e.g., xe2x80x94CF3 and xe2x80x94CH2CF3) and acyl (e.g., xe2x80x94C(O)CH3, xe2x80x94C(O)CF3, xe2x80x94C(O)CH2OCH3, and the like).
Similarly, substituents for the aryl groups are varied and are selected from: -halogen, xe2x80x94ORxe2x80x2, xe2x80x94OC(O)Rxe2x80x2, xe2x80x94NRxe2x80x2Rxe2x80x3, xe2x80x94SRxe2x80x2, xe2x80x94Rxe2x80x2, xe2x80x94CN, xe2x80x94NO2, xe2x80x94CO2Rxe2x80x2, xe2x80x94CONRxe2x80x2Rxe2x80x3, xe2x80x94C(O)Rxe2x80x2, xe2x80x94OC(O)NRxe2x80x2Rxe2x80x3, xe2x80x94NRxe2x80x3C(O)Rxe2x80x2, xe2x80x94NRxe2x80x3C(O)2Rxe2x80x2, xe2x80x94NRxe2x80x2xe2x80x94C(O)NRxe2x80x3Rxe2x80x2xe2x80x3, xe2x80x94NHxe2x80x94C(NH2)xe2x95x90NH, xe2x80x94NRxe2x80x2 C(NH2)xe2x95x90NH, xe2x80x94NHxe2x80x94C(NH2)xe2x95x90NRxe2x80x2, xe2x80x94S(O)Rxe2x80x2, xe2x80x94S(O)2Rxe2x80x2, xe2x80x94S(O)2NRxe2x80x2Rxe2x80x3, xe2x80x94N3, xe2x80x94CH(Ph)2, perfluoro(C1-C4)alkoxy, and perfluoro(C1-C4)alkyl, in a number ranging from zero to the total number of open valences on the aromatic ring system; and where Rxe2x80x2, Rxe2x80x3 and Rxe2x80x2xe2x80x3 are independently selected from hydrogen, (C1-C8)alkyl and heteroalkyl, unsubstituted aryl, (unsubstituted aryl)-(C1-C4)alkyl, (unsubstituted aryl)oxy-(C1-C4)alkyl and perfluoro(C1-C4)alkyl.
Two of the substituents on adjacent atoms of the aryl ring may optionally be replaced with a substituent of the formula xe2x80x94Txe2x80x94C(O)xe2x80x94(CH2)qxe2x80x94Uxe2x80x94, wherein T and U are independently xe2x80x94NHxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94CH2xe2x80x94 or a single bond, and the subscript q is an integer of from 0 to 2. Alternatively, two of the substituents on adjacent atoms of the aryl ring may optionally be replaced with a substituent of the formula -A-(CH2)r-B-, wherein A and B are independently xe2x80x94CH2xe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94S(O)xe2x80x94, xe2x80x94S(O)2xe2x80x94, xe2x80x94S(O)2NRxe2x80x2xe2x80x94 or a single bond, and r is an integer of from 1 to 3. One of the single bonds of the new ring so formed may optionally be replaced with a double bond. Alternatively, two of the substituents on adjacent atoms of the aryl ring may optionally be replaced with a substituent of the formula xe2x80x94(CH2)sxe2x80x94Xxe2x80x94(CH2)txe2x80x94, where s and t are independently integers of from 0 to 3, and X is xe2x80x94Oxe2x80x94, xe2x80x94NRxe2x80x2xe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94S(O)xe2x80x94, xe2x80x94S(O)2xe2x80x94, or xe2x80x94S(O)2NRxe2x80x2xe2x80x94. The substituent Rxe2x80x2 in xe2x80x94NRxe2x80x2xe2x80x94 and xe2x80x94S(O)2NRxe2x80x2xe2x80x94 is selected from hydrogen or unsubstituted (C1-C6)alkyl.